Research during the next year will focus on several projects. We will try to resolve the paradox as to why C.AL-20 congenic mice, which have the H chain allotype of the AL/N strain on a BALB/c background, produce antibodies to the phenylarsonate (Ar) hapten which have the intrastrain cross-reactive idiotype (CRI) characteristic of the AL/N strain, despite the need for appropriate L chains and the probable absence of linkage between genes coding for L and H chains. This question will be approached by structural analysis of the L chains of idiotypic molecules in C.AL-20 mice and comparison with those of the A strain, and with L chains of BALB/c anti-Ar antibodies. A second approach will be to produce F1 hybrids of strain A and another nonidiotype producing strain (strain B). The F1 mice will be back-crossed to B mice and we will determine whether all offspring with the strain A heavy chain allotype also produce the cross-reactive idiotype; i.e., whether strain B can provide appropriate L chains. Another investigation will examine the question as to when the CRI discussed above appears during ontogeny. This will be approached through adoptive transfers of splenic cells from neonatal A/J mice into lethally irradiated recipients. If, as appears probable, the CRI is a product of a germ line gene, it should appear very early in the ontogeny of the mouse. We will also attempt to extend to larger animals our finding that substantial quantities of ascitic fluids, containing high titers of antibodies, can be produced in mice by an appropriate, frequent schedule of inoculations of antigen in Freund's adjuvant. Results with the guinea pig appear very promising.